SiOx monolayer overcoating effect on the TiO2 photocatalytic oxidation of cetylpyridinium bromide

The effect of SiOx monolayer coverage on the rate of TiO2 photocatalytic oxidation of cetylpyridinium bromide (CPB) in aqueous solutions has been studied. The rate of CPB removal from the solution (5 < pH < 7) increases with the surface modification at concentrations below 4.5 x 10(-4) M and its promoting effect is enhanced with decreasing concentration. A modified Langmuir-Hinshelwood model, where the rate of surface reaction is assumed to be proportional to the coverage of CPB at the photostationary state is proposed for dilute reaction systems, As a result of the kinetic analyses, the acceleration of the reaction with the SiOx monolayer coverage can be attributed to the increase in the rate of adsorption due to the electrostatic attraction of cetylpyridinium ion. The suppression of Br- adsorption is also suggested as a minor contribution. (C) 2000 Academic Press.